Methane Emission Reductions in Oil and Gas Processing

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1 Methane Emission Reductions in Oil and Gas Processing EPA Middle East Meeting Washington, D.C. 2 October 2012 Don Robinson ICF International Vice President

2 Agenda U.S. Processing Sector Methane Emissions Overview of Technologies and Practices Methane Saving Opportunities Compressors Leak detection, quantification, and repair Acid gas removal Contacts and Further Information 1

3 2010 U.S. Processing Sector Methane Emissions (1.2 Bcm) Blowdowns 60 MMcm 5% Plant Fugitives 42 MMcm 4% Dehydrators and Pumps 23 MMcm 2% AGR Vents 17 MMcm 1% Other Sources 2 MMcm 0% Gas Engine Exhaust 224 MMcm 18% Reciprocating Compressors 515 MMcm 42% Centrifugal Compressors 342 MMcm 28% EPA. Inventory of U.S. Greenhouse Gas Emissions and Sinks April,

4 Emissions Sources in Gas Gathering/Processing Plants VC Dehydrator Compressor Drain Valve DC LC Energy Exchange Pump FC FTS LC Reboiler TC LC PC FC PC Compressor Seal Pressure Relief Valve Pneumatic Controller 3

5 Overview of Technologies and Practices 30 technologies and practices that apply to the processing sector Reduce compressor venting with fewer startups Begin leak detection, quantification and repair at processing plants Eliminate unnecessary equipment and/or systems Pipe glycol dehydrator to vapor recovery unit Inspect and repair compressor station blowdown valves Convert gas-driven pneumatic devices to instrument air Economic replacement of rod packing in reciprocating compressors Install pressurized storage of condensate Alternate acid gas removal technologies Replace high-bleed pneumatic devices with low-bleed devices 4

6 Reciprocating Compressor Emissions Overview Reciprocating compressors rod packing leaks some gas by design Flexible rings fit around the shaft to minimize leakage Leakage still occurs through nose gasket, between packing cups, and between rings and shaft Emissions can range between 0.3 to 25 m 3 /hour depending on age of packing 5

7 Reciprocating Compressor Emission Reductions Methane emissions can be reduce through economic replacement of rod packing Measure rod packing leakage periodically over life of packing Determine cost of packing replacement Determine economic replacement threshold Compare value of excess gas lost with worn packing to savings with new packing Replace packing when leak reduction will pay back cost 3 Economic Replacement Threshold (m /hr) Where: CR = Cost of replacement DF = Discount factor at interest i, over period n H = Hours of operation GP = Gas price per thousand cubic meters CR DF 1000 H GP n i(1 i) DF n (1 i) 1 6

8 Centrifugal Compressor Emissions Overview Centrifugal Compressors have seals around rotating shaft to prevent gas from escaping Seals often use oil, called wet seals The majority of methane emissions occur through seal oil degassing which is often vented to the atmosphere Oil is very effective at preventing leaks but also entrains a substantial amount of gas Emissions from seal oil degassing vents can range between 1.1 to 5.7 m 3 /minute 7

9 Centrifugal Compressor Emission Reductions Converting wet seals to dry seals can drastically cut methane emissions Dry seal springs press stationary ring in seal housing against rotating ring At high rotation speed, gas is pumped between seal rings creating a high pressure barrier to leakage Only a very small amount of gas escapes through the gap (0.01 to 0.08 m 3 /min) Another alternative is to set up a vapory recovery system to capture vented methane from wet seals Highly effective captures up to 99% of otherwise vented gas Requires less compressor downtime to set up Easy to set up on older wet seal compressors 8

10 Leak Detection, Quantification, and Repair Directed Inspection and Maintenance (DI&M) Cost-effective practice, by definition Find and fix significant leaks Strictly tailored to company s needs Real-time detection of methane leaks using infrared technology Quicker identification & repair of leaks Screen hundreds of components an hour Screen inaccessible areas simply by viewing them Identified leaks can be measured by a Hi Flow sampler, calibrated bag, turbine meter, or other technology 9

11 Component Count vs. Emissions Distribution of component count and estimated emissions by screening range Source: Robinson, et al. Refinery Evaluation of Optical Imaging to Locate Fugitive Emissions. Journal of Air and Waste Management. Volume 57, July

12 Is Recovery Profitable? Repair the Cost-Effective Components Component Annual Value of Lost Gas ($) Estimated Repair Cost ($) Payback (months) Plug Valve: Valve Body 12, Union: Fuel Gas Line 12, Threaded Connection 10, Distance Piece: Rod Packing 7,650 2, Open-Ended Line 6, Compressor Seals 5,784 2, Gate Valve 4, Source: Hydrocarbon Processing, May 2002 Based on $3/MMBtu gas price 11

13 Acid Gas Removal (AGR) What is the Problem? Wellhead natural gas may contain acid gases Hydrogen sulfide (H 2 S) and CO 2 are corrosive to pipelines, compressors, instruments, and distribution equipment Acid gas removal processes have traditionally used an aqueous amine solution to absorb acid gas These solutions absorb methane along with the acid gases Amine regeneration strips acid gas and absorbed methane If the acid gas is CO 2 it is typically vented to the atmosphere, flared, or recovered for enhanced oil recovery (EOR) H 2 S is typically flared (low concentrations) or sent to the sulfur recovery unit (high concentrations) There are two commercial alternatives to DEA absorption Membrane Molecular Gate 12

14 AGR Alternatives: Membrane Separator Membrane separation of CO 2 from feed gas High CO 2 permeate (effluent or waste stream) exiting the membrane is vented or blended into fuel gas Low CO 2 product exiting the membrane exceeds pipeline spec and is blended with feed gas Bypass for Fuel Fuel Gas Spec Aerosol Separators High CO 2 Permeate Feed Gas MEMBRANE UNIT Pipeline Spec (trace lube, glycol, etc. removal) Bypass for Blending Adapted from Trimming Residue CO 2 with Membrane Technology, OGJ

15 Membrane Economics: Is Recovery Profitable? Cost comparison DEA AGR cost $4.5 to $5 million capital, $0.5 million operation and maintenance (O&M) per year Membrane process cost $1.5 to $1.7 million capital, $0.02 to $0.05 million O&M per year Optimization of permeate stream Permeate mixed with fuel gas, $175/Mcm fuel credit Only install enough membranes to take feed from >3% to <2% CO 2 Expand with additional membranes 14

16 AGR Alternatives: Molecular Gate Molecular Gate adsorbs acid gas (CO 2 and H 2 S) in fixed bed Molecular sieve application selectively adsorbs acid gas molecules of smaller diameter than methane Bed regenerated by depressuring 10% of feed methane lost in depressuring Route tail gas to fuel Applicable to lean gas sources 15

17 Molecular Gate Economics: Is Recovery Profitable? Molecular Gate costs are 20% less than amine process Fixed-bed tail gas vent can be used as supplemental fuel Eliminates venting from acid gas removal Other Benefits Allows wells with high acid gas content to produce (alternative is shut-in) Can dehydrate and remove acid gas to pipeline specs in one step Less operator attention 16

18 Comparison of AGR Alternatives Amine (or Selexol TM ) Process Kvaerner Membrane Molecular Gate CO 2 Absorbent or Adsorbent Water & amine (Selexol TM ) Cellulose acetate Titanium silicate Methane Savings Compared to Amine Process -- Methane in permeate gas combusted for fuel Methane in tail gas combusted for fuel Regeneration Reduce pressure & heat Replace membrane about 5 years Reduce pressure to vacuum Primary Operating Costs Amine (Selexol TM ) & steam Nil Electricity Capital Cost 100% 35% <100% Operating Cost 100% <10% 80% 17

19 Contact and Further Information Don Robinson ICF International Vice President +1 (703) Global Methane Initiative globalmethane.org Recommended Technologies (Arabic) epa.gov/gasstar/tools/arabic/index.html 18